STEPHENVILLE, Texas (AP) — A jury's rejection of the insanity defense of a former Marine in the deaths of famed "American Sniper" author Chris Kyle and another man illustrates the difficulty of succeeding with such a defense.

After a two-week trial in which jurors heard testimony about defendant Eddie Ray Routh's erratic behavior, including statements about anarchy, the apocalypse and pig-human hybrids, they convicted Routh Tuesday night in the deaths of Kyle and Chad Littlefield at a Texas shooting range two years ago.

Routh's trial drew intense interest, in part because of the blockbuster film based on former Navy SEAL Kyle's memoir about his four tours in Iraq.

"The insanity defense is very rare, and it's even rarer that a defendant wins it," said George Dix, a law professor at the University of Texas at Austin.

He said when a brutal crime is committed it's difficult to convince a jury that the person accused doesn't "deserve the condemnation that comes from a finding of guilty." He added, "And here, we've got him causing the death of an American hero."

The verdict in Texas came at a time when a Colorado court is preparing to hear similar arguments in the trial of James Holmes over a 2012 movie theater shooting in which 12 people were killed.

Texas juror Christina Yeager told ABC's "Good Morning America" that Routh displayed a similar pattern in prior run-ins with police — he would become intoxicated and then tell responding officers he was a victim of post-traumatic stress disorder. "Every time something bad happened he pulled that card," Yeager said.

Barrett Hutchinson said jurors were not convinced by the claim that Routh was having a psychotic episode when he shot the men.

"He knew the consequences of pulling the trigger," Hutchinson said.

Routh showed no reaction as a judge sentenced him to life in prison without parole, an automatic sentence since prosecutors didn't seek the death penalty in the capital murder case. As one of his victim's siblings called him an "American disgrace" shortly after, Routh looked back at the man intensely but didn't react otherwise.

The verdict capped an emotional trial in which prosecutors painted the 27-year-old as a troubled drug user who knew right from wrong, despite any mental illnesses. Defense attorneys said he suffered from schizophrenia and was suffering a psychotic episode at the time of the shootings. While trial testimony and evidence often included Routh making odd statements and referring to insanity, he also confessed several times, apologized for the crimes and tried to evade police after the crime.

Kyle and Littlefield had taken Routh to the shooting range at Rough Creek Lodge and Resort on Feb. 2, 2013, after Routh's mother asked Kyle to help her troubled son. Family members say Routh suffered from post-traumatic stress disorder from serving in Iraq and in Haiti after the devastating 2010 earthquake.

A forensic psychologist testified for prosecutors that Routh was not legally insane and suggested he may have gotten some of his ideas from television. Dr. Randall Price said Routh had a paranoid disorder made worse by his use of alcohol and marijuana, calling his condition "cannabis-induced psychosis."

Defense attorneys noted that Kyle had described Routh as "straight-up nuts" in a text message to Littlefield as they drove to the luxury resort. They said Routh, who had been prescribed anti-psychotic medication often used for schizophrenia, believed the men planned to kill him.

Routh's defense team said they would appeal the conviction.